Migrate to JSON i18n

Procedure per https://www.mediawiki.org/wiki/Manual:GenerateJsonI18n.php
with shim.

Also reindent a JavaScript file that made the tests fail, and add a
.jshintignore with a FIXME to not make that happen again.

Change-Id: I3f35a87e3b8ebeae08b893d65cc0034587f85697